The present invention relates to a transmitter of a tire condition monitoring apparatus. More particularly, the present invention pertains to a transmitter for a wireless tire condition monitoring apparatus that permits a driver in a vehicle passenger compartment to check conditions of tires, such as the air pressure.
Wireless tire condition monitoring apparatuses that allow a driver in a vehicle passenger compartment to check the conditions of vehicle tires have been proposed. For example, Japanese Laid-Open Patent Publication No. 2001-174357 discloses such an apparatus. The apparatus of the publication includes transmitters and a receiver. Each transmitter is located in the wheel of one of the tires and the receiver is located in the body frame of the vehicle. Each transmitter detects the conditions, such as air pressure and the temperature of the associated tire, and wirelessly transmits the detected information. The receiver receives data wirelessly transmitted by the transmitters with an antenna and displays the conditions of the tires, for example, on a display located in front of the driver's seat.
Each transmitter is accommodated in a case provided in the corresponding tire valve. The tire valve is fitted in a valve hole of the corresponding wheel. Accordingly, the case, which accommodates the transmitter, is located in the corresponding tire.
The wheels are formed of metal, such as aluminum and iron. Metal bead wire is embedded in sidewalls of each tire for reinforcing the tire. Thus, radio waves transmitted by the transmitters are attenuated by the wheels and the bead wire. As a result, the probability that the receiver receives data wirelessly transmitted by each transmitter, or the reception probability, is reduced.